0.84 gm/m3 water concentration means roughly 0.84 ml/m3 in volume assuming water density to be 1 g/ml, or 1000 g/litre. this makes that for 1 m3 of the mixture there is o.84 ml or 0.84x10-6 m3. the volume fraction of water would be (0.84x10-6 m3)/(1 m3) that is 0.84x10-6. Hope this helps.